1) Field of the Invention
The present invention relates to a process for producing the trans-isomer of 1,4-bis(aminomethyl)cyclohexane and more particularly concerned with a process for producing a higher content of trans 1,4-bis(aminomethyl)cyclohexane from a mixture of the cis isomer and trans isomer.
2) Description of the Prior Art
1,4-bis(aminomethyl)cyclohexane is an industrially important compound as a raw material for polyamides. Diisocyanate obtained from the 1,4-bis(aminomethyl)cyclo-hexane is useful as a raw material for polyurethanes.
1,4-bis(aminomethyl)cyclohexane has two stereoisomers of trans isomer and cis isomer and the content of trans-isomer influences the physical properties of the polyamides and polyurethanes.
For instance, in the case of polyamides produced from 1,4-bis(aminomethyl) cyclohexane and suberic acid, the higher content of trans-isomer improves melting point and heat stability. So more favorable polymers for fibers, films and plastic elements are obtained by using a higher content of trans-isomer. In the case of polyurethanes produced from polyalcohols and diisocyanate derived from 1,4-bis(aminomethyl)cyclohexane, higher content of trans isomer improves solubility in solvents.
So, it is expected to develop a process for producing more valuable 1,4-bis(aminomethyl)cyclohexane which contains more trans 1,4-bis(aminomethyl) cyclohexane.
1,4-bis(aminomethyl)cyclohexane is produced generally by hydrogenation of p-xylylenediamine. The selective production of trans isomer in this process is difficult because more cis isomer is produced than trans isomer. The content of trans isomer in this process is less than 40%, so the isomerization method or separation method to obtain the product may be considered to produce a higher content of trans-isomer of 1,4-bis(aminomethyl)cyclohexthane.
Concerning isomerization of the alicyclic amines, isomerization of bis(4-aminocyclohexyl)methane which has three stereoisomers of trans-trans type, cistrans type and cis-cis type is known. Methods of increasing the content of bis(4-aminocyclohexyl)methane of trans-trans type by isomerization by heating higher than 130.degree. C. using a catalyst of ruthenium oxide, nickel or cobalt and hydrogen are disclosed in Japanese Patent Publication No. 46-16979 and Japanese Patent Publication No. 46-30835. In U.S. Pat. No. 4058568, there is described a method for producing a higher content of trans-trans bis(4-aminocyclohexyl) methane by synthesizing an imine compound from bis(4-aminocyclohexyl)methane and benzaldehyde, isomerizing the imine compound with alkali catalyst and hydrolyzing the isomerized imine compound with acid.
As the separation method for producing higher content of trans 1,4-bis(aminomethyl)cyclohexthane, the distillation method or crystallization method may be considered. However, in general, the distillation method requires a multi-stage distillation column to separate cis isomer and trans isomer because the boiling points of these isomers are very close.
Although the separation method of crystallization and the content of trans isomer are not disclosed, it is described in the Japanese magazine Yuuki Gosei Kagaku (Organic Chemistry) vol. 25, No. 2 page 46 (1967) that the amount of white crystals obtained is increased by keeping 1,4-bis(aminomethyl)cyclohexane at 0 to -5.degree. C. and the peak of the trans isomer obtained by gas chromatography of these white crystals become large.
However, when this method is used with 1,4-bis(aminomethyl)cyclohexthane which is produced by hydrogenation of p-xylylene diamine and the content of trans isomer is less than 40%, the yield of trans isomer is very low because mutual solubilities of two isomer are large. Even if the recovery from the mother liquor is repeated, more than 60% of 1,4-bis(aminomethyl)cyclohexane remains as cis isomer theoretically.
The first object of the present invention is to increase the content of trans isomer of 1,4-bis(aminomethyl)cyclohexthane which is generally produced by hydrogenation of p-xylylene diamine and is used as a raw material for polyamide and polyurethane products that have excellent physical or chemical properties.
The second object of the present invention is to provide a method to obtain 1,4-bis(aminomethyl)cyclohexane containing more than 80% of trans isomer with high yield from bis(aminomethyl)cyclohexane containing the cis and trans isomers.